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What do charge controllers do?

There are many variables that affect how much power is generated by your panels at any given time, including the level of sunlight, temperature, and your battery’s state of charge. Charge controllers, which sit between the solar panels and battery bank, perform the essential role of monitoring all these factors to ensure the optimal amount of energy from your panels gets fed into your battery bank. This ensures your system runs efficiently and safely. Solar charge controllers also prevent battery drainage by shutting down the system if stored power falls below 50 percent capacity. This helps preserve the life and health of the batteries.


What are the different types of solar charge controllers?

There are two types of charge controllers to consider: Pulse Width Modulation (PWM) controllers and Maximum Power Point Tracking (MPPT) controllers. PWM charge controllers are an older technology and are cheaper, but less efficient than MPPT charge controllers. Both are widely used, have similar lifespans, and preserve the life of your batteries. 


The main benefit of MPPT controllers is that they actively monitor and adjust their input to regulate a solar system’s current, and they will step down the voltage and boost the current. For example, if it becomes cloudy, your MPPT charge controller will automatically decrease the amount of current drawn in order to maintain a desirable voltage at the output of the panel. When it becomes sunny again, the MPPT controller will allow more current in again. With these functionalities at work, you can expect efficiency ratings of 90% or higher. 


PWM charge controllers are the cheapest charge controller option, best for warm sunny weather, and performs best when the battery is near the full state of charge. PWM controllers regulate the flow of energy to the battery by reducing the current gradually, called "pulse width modulation.” When batteries are full, a PWM charge controller will supply a tiny amount of power to keep batteries full. 


What size solar charge controller do I need?

Charge controllers are sized based on the solar array's current and the solar system’s voltage. You typically want to make sure you have a charge controller that is large enough to handle the amount of power and current produced by your panels. If your solar system's volts were 12 and your amps were 14, you would need a charge controller that had at least 14 amps. However, due to environmental factors, you need to factor in an additional 25%. This brings the minimum amps that this charger controller must have to 17.5 amps. In this example, you would need a 12 volt, 20 amp charge controllers. We recommend using the Renogy solar calculator to determine what size solar installation you need to meet your energy needs.